1. Field of the invention
The present invention relates generally to lamp drives, and more particularly to a lamp drive having a shutdown interface circuit.
2. Description of the Background of the Invention
Lamp drivers have been devised that provide power to one or more lamp loads, such as one or more LEDs arranged in one or more modules. The LEDs, particularly of late, develop a very bright light output but consume relatively little power compared to other types of lamps that develop a comparable light output brightness.
Prior lamp drivers have utilized electromechanical contactors that are responsive to a shutdown signal supplied by a user-operable switch to deactuate the lamp(s). While these types of drivers have been useful to allow a lamp load to be shut down, the use of electromechanical contactors has been problematic in that the contactors are expensive, subject to failure, and contribute to operational cost.
The International Electrotechnical Commission (IEC) has published standard 60929, Annex E, entitled “Control Interface for Controllable Ballasts” (© IEC:2006) that specifies operational parameters for controllable ballasts. The specification recites that the controllable ballast must be responsive to an input control signal across input conductors that varies in a control range between zero volts and 11 volts to operate a lamp connected to the ballast in a stable manner so that the lamp develops stable light output. The IEC standard further specifies that as the input control signal varies between 1 and 10 volts, the arc power of the controllable ballast must similarly vary between minimum and maximum values. Still further, the controllable ballast must also be capable of operating as a current source and must be operable with any voltage between −20 V and +20 V across the input conductors without damage.
While the IEC standard is effective to specify the design of a controllable ballast, no provision is supplied for shutting down a lamp controlled by the ballast.